Oxidation selectivity between n-hexane and sulfur dioxide in diesel simulated exhaust gas over platinum-supported zirconia catalyst

We examined the oxidation reaction of n-C6H14 and SO2 over two types of Pt/ZrO2 catalysts with low (8 m2/g) and high (75 m2/g) surface areas of the ZrO2 supports (referred to as ZrO2-8 and ZrO2-75, respectively). The catalytic activity was evaluated under simulated diesel exhaust gas which simultaneously contained n-C6H14 and SO2. The Pt/ZrO2-75 exhibited a desirably higher selectivity for the complete oxidation of n-C6H14 than that of SO2, as compared with the Pt/ZrO2-8. In order to clarify the cause of this selective oxidation, we investigated the Arrhenius parameter for these oxidation reactions and characterized these catalysts using X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), Transmission electron micrograph (TEM), IR and CO2 temperature-programmed desorption (CO2-TPD) methods. The amount of Pt0 (metal) in the Pt/ZrO2-75 was significantly lower than that in Pt/ZrO2-8, because the high basicity of the ZrO2-75 support stabilized the high oxidation state of Pt such as Pt2+ and Pt4+. It was concluded that the difference in the number of Pt0 sites as catalytic active sites causes the apparent selectivity to change due to the much slower reaction rate for the SO2 oxidation than that for the n-C6H14 oxidation.